science Physical Lab Instructions
If you have the physical polaroid films, follow these steps to enact the roles of Alice, Bob, and Eve.
Setup & Roles
Assign one person as Alice (Sender) and one as Bob (Receiver). You need a light source (flashlight) and two polaroid films.
Alice: Sending a Photon
Alice chooses a Bit (0 or 1) and a Basis (+ or X). She holds her film in front of the light in the corresponding orientation:
Bob: Measuring
Bob independently chooses a basis (+ or X) and holds his film in that orientation. He looks through both films (Alice's + His) at the light.
The Result
- Bright Light: The polarizations match. Bob records the bit corresponding to his film's angle.
- Darkness: The polarizations are opposite (e.g., Vert vs Horiz). This is the 'inverse' bit.
- Grey/Dim Light: Bases Mismatch! (e.g., Vertical vs Diagonal). The photon has a 50% chance of passing. This represents "Randomness".
visibility Adding Eve (The Eavesdropper)
Eve inserts a third film between Alice and Bob. This represents interception. Notice how Eve's film changes the light intensity Bob sees! If Eve uses the wrong basis, she dims the light (collapsing the state) before it reaches Bob, introducing potential errors.
play_circle Digital Simulation
Run the experiment virtually to generate data.
lightbulb Key Quantum Principles
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psychology
Uncertainty Principle
If Eve uses the wrong basis (e.g., measuring a Rectilinear photon with a Diagonal filter), she permanently alters its state.
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warning
Irreversible Disturbance
When Bob measures this disturbed photon, he has a 50% chance of an error, even if he uses the correct basis. This is how we detect eavesdropping!
The Characters
Alice
Sender
Eve
Spy
Bob
Receiver